1. Field of the Invention
This invention relates to water treatment processes. More particularly, the present invention is directed to a process for removing perchlorate ions from waste water.
2. Technology Background
Ammonium perchlorate (abbreviated "AP", having the chemical formula NH.sub.4 ClO.sub.4) is a common waste stream ingredient in the processing and reclamation of solid rocket propellants. Because solid rocket motors often include 60% AP, water used to wash and clean rocket motor processing facilities and equipment typically contain up to about 100,000 parts-per-million (ppm) AP.
There are three approaches that have been used in the industry for disposing of waste streams containing AP. In the first approach, the waste water is treated to remove high energy materials, such as NG, HMX or RDX, and the waste stream is discharged for treatment by a municipal or privately owned water treatment facility. The perchlorate is not treated but is diluted. In the another approach, a third party, such as a slurry explosive company, is paid to evaporate the water from the waste stream leaving a concentrated AP slurry capable of use as in the mining industry as a slurried explosive. There is also a patented bio-digestion process for low level treatment of AP. There still remains a need in the art for a process of removing AP from waste streams.
Applicant is aware of an unpublished a process of treating waste streams containing AP in concentrations exceeding 10,000 ppm. The treatment chemistry is shown below: ##STR1##
In the process, waste perchlorate is concentrated by water evaporation. During the concentrating step, ammonia and volatile organics are also removed. Potassium hydroxide (KOH) is added to the perchlorate salts which converts the perchlorate to potassium perchlorate (KClO.sub.4).
To prevent the potassium perchlorate from crystallizing prematurely, it is necessary to keep the concentrated mixture at an elevated temperature until it reaches the crystallizers. Once in the crystallizers, the reaction mixture is cooled and the potassium perchlorate precipitates from solution. The precipitated potassium perchlorate is dewatered, and the crystallizing liquor is routed for further treatment.
KOH is a preferred reactant in this process because the hydroxide counterion does not further contaminate the reaction stream, but forms water. The high pH resulting from the hydroxide ions also facilitates ammonia removal. Finally, being a liquid, KOH is easier to handle than a solid because it can be pumped.
Although effective for its intended purpose, there are significant disadvantages with the above-described perchlorate removal process. For instance, concentrated KOH (pH=14) is hazardous and corrodes process equipment and pipes. Even after removal of precipitated KClO.sub.4, remaining hydroxide ions in the waste water and on the KClO.sub.4 crystals must be neutralized with acid. Until neutralization is completed, the high pH solutions pose a personnel safety issue. Moreover, concentrating the perchlorate is an important step in the process, but because KOH used in the process is liquid, with a maximum concentration of 40% dilution of the perchlorate solution occurs when the KOH is added. This dilution results in more waste water to be processed and a lower yield of KClO.sub.4.
From the foregoing, it will be appreciated that there is a need in the art for a perchlorate ion removal process which is not hazardous or corrosive and which does not require pH neutralization. It would also be a significant advancement in the art to provide a perchlorate ion removal process which does not dilute the perchlorate solution, but results in high perchlorate yield.
Such a process for removing perchlorate ion from waste water is disclosed and claimed herein.